2013 Mac Pro and USB 3.0 Hubs:
Not sure how many this affects (as there's been issues with some USB 3.0 hubs with other Macs), but a reader asked I post a FYI on an issue booting a new Mac Pro (Late 2013) if a USB 3.0 Hub was connected at powerup. His notes on tests with two USB 3.0 hubs are in this Apple forum thread on New Mac Pro (late 2013) USB 3.0 hub issue during boot. However later replies in that thread from other Late 2013 Mac Pro owners said they've not seen any issues with USB 3.0 hubs, including one owner using the same hub model.